The Science

The ScienceThe need for a continuous energy supply and energy requirements for transportation necessitates technology for storage of energy from sunlight in fuel, as well as conversion to electricity. Cost-effective technologies for solar fuel production do not exist, prompting the need for new fundamental science.

Fuel production requires not only energy, but also a source of electrons and precursor materials suitable for reduction to useful fuels. Given the immense magnitude of the human energy requirement, the most reasonable source of electrons is water oxidation, and suitable precursor materials are hydrogen ions (for hydrogen gas production) and carbon dioxide (for reduced carbon fuel production). Natural photosynthesis harvests solar energy on a magnitude much larger than that necessary to fill human needs. It does so using antenna-reaction center systems that collect sunlight and convert it to electrochemical energy via formation of charge-separated species. This electrochemical potential is coupled to an enzymic catalyst for water oxidation, and to catalysts for reductive chemistry that produce biological fuels such as carbohydrate, lipid, or molecular hydrogen.

The Center for Bio-inspired Solar Fuel Production (BISFUEL) approaches the design of a complete system for solar water oxidation and hydrogen production by applying the fundamental design principles of photosynthesis to the construction of synthetic components, and their incorporation into an operational unit. The functional blueprint of photosynthesis are being followed, using non-biological materials.

Collection of sunlight and conversion to electrochemical potential will be performed by artificial antenna-reaction centers based on their natural analogs. These will be constructed using the tools of organic chemistry and components such as porphyrins, fullerenes, and carotenoid polyenes. They will incorporate light harvesting (absorption and energy transfer), charge separation (photoinduced electron transfer), photoprotection and regulation.

Water oxidation complexes will be based on a unique, self-assembling, engineered DNA nanostructure that organizes short synthetic peptides arranged in a manner analogous to the natural oxygen-evolving complex. These peptides will be used to construct a metal-ion-based catalytic site similar to the natural one, using assembly methods found in photosynthesis. In a second approach, peptide-based water-soluble analogs of the natural photosynthetic oxygen-evolving complex will be sought. The DOE ALS in Berkeley will be used for X-ray (as necessary), XAFS and XANES characterization of the artificial water oxidation (and proton reduction) catalysts.

Hydrogen production catalysts will be based on natural hydrogenase enzymes. Iron-containing catalytic sites and iron-sulfur sites for storing reduction equivalents will be organized into functional catalysts using metal nanoparticles and linked to transparent electrodes.

New transparent, nanostructured, high-surface-area conducting metal oxide materials will be constructed to serve as functional frameworks for organizing the various components of the system, separating mutually reactive intermediates, and facilitating electrical communication among components.

A major challenge is the integration of the various components mentioned above into a functional system that is competent to carry out water splitting as a unit. This will require careful attention both to the thermodynamic and kinetic properties of the catalysts and charge-separation units and to the transport of redox equivalents and materials among the various units of the complex. Thus, the research has a strong systems engineering component. Two photosystems, à la photosynthesis, will likely be necessary to achieve useful efficiencies. Initially, metallic connections between some subsystems will be used in order to permit testing of components electrochemically and application of external emf as necessary. Based on the performance of natural photosynthesis, the synthetic system has the potential to produce fuel efficiently from sunlight and water, to be inexpensive, to use earth-abundant elements, and to be a practical solution to humanity’s energy problems. Realizing this potential is a significant fundamental and applied scientific challenge.

While pursuing this ambitious goal, the Center will uncover basic scientific knowledge that will point the way to new catalysts for water splitting and fuel cells, new materials for solar photovoltaics of various kinds, new ways to use DNA and peptides for preparation of artificial enzymes for biomedical and other technological applications, and new fundamental ways of understanding and manipulating matter that will have applications in many different areas of technology. It may also help identify ways to modify natural photosynthesis in plants so that it can better fill humanity’s needs.

Center for Bio-Inspired Solar Fuel Production 
Arizona State University, Room ISTB-5 101, Box 871604, Tempe, AZ 85287-1604 
phone: (480) 965-1548 | fax: (480) 965-5927 | Contact Us